Thermally zoned substrate holder assembly

ABSTRACT

A thermally zoned substrate holder including a substantially cylindrical base having top and bottom surfaces configured to support a substrate. A plurality of temperature control elements are disposed within the base. An insulator thermally separates the temperature control elements. The insulator is made from an insulting material having a lower coefficient of thermal conductivity than the base (e.g., a gas-or vacuum-filled chamber).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority to U.S. ProvisionalApplication Ser. No. 60/429,540, filed Nov. 29, 2002. The entirecontents of this application are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a thermally-zoned substrateholder for maintaining the temperature of the surface of a substrateduring processing in a plasma system, and more particularly to asubstrate holder including thermal insulation separating multipletemperature controlled zones.

2. Discussion of the Background

It is known in semiconductor manufacturing that processing systems oftenuse and, in many cases, require the incorporation of temperature controlelements to control both wall and substrate temperatures and ensurerobust substrate processing. For example, temperature control elementscan include resistance heaters to heat a substrate holder which supportsa semiconductor substrate during a processing step or steps, or to heatthe chamber walls in order to reduce residue formation duringprocessing. Moreover, temperature control elements can include fluidchannels designed to carry either heated or cooled fluid to and from thesubstrate holder or chamber wall in order to deposit heat in theprocessing system or extract heat from the processing system. Ingeneral, the substrate temperature as well as the chamber walltemperature, and their respective spatial uniformities, can have aprofound influence on the process results.

One example of a substrate holder comprising temperature controlelements is shown in FIG. 1. As illustrated in FIG. 1, a substrateholder 11, typically fabricated from aluminum, includes a temperaturecontrol element 17, such as a cooling channel or a heating element whichgenerally takes the form of a loop. In some case, heat transfer fins canextend from an internal surface of the temperature control element 17 inthe substrate holder 11 in order to effectively increase the wettedsurface area through which heat is exchanged between the substrateholder 11 and the temperature control element 17.

SUMMARY OF THE INVENTION

Therefore, a need exists for an apparatus and method for providingmultiple insulated thermal zones in either a metallic or non-metallicsubstrate holder. A need further exists for such an apparatus and methodto be simply and inexpensively installed and maintained.

Accordingly, it is an object of the present invention to create multipleinsulated thermal zones in a substrate holder to better tailor featuresto the cooling and heating processes thereof. The distinctly separatetemperature controlled passages and heating elements create multipletemperature zones in the substrate holder that allow the temperaturecontrolling mechanisms in the substrate holder to be utilizedeffectively.

According to one embodiment of the present invention, a thermallyinsulating material is inserted between cooling passages to formindependently controllable temperature zones. Such thermal insulatorscan be any material or combination of materials with a low heat transfercoefficient (e.g., air or vacuum).

In addition, reflecting surfaces on the outer surfaces of the thermalinsulator can be utilized. These reflective surfaces can be produced inmany different ways, including but not limited to foil, sputtering andsurface treatments. The reflecting surfaces further hinder the heattransfer characteristics of the thermal insulator.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will become readily apparent to those skilled in theart with reference to the following detailed description particularlywhen considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a known substrate holder;

FIG. 2A is a top view of a substrate holder according to the presentinvention;

FIG. 2B is a side view of a substrate holder according to the presentinvention;

FIG. 2C is a cross-sectional view of a substrate holder according to thepresent invention;

FIG. 2D is a bottom view of a substrate holder according to the presentinvention;

FIG. 3 is a cross-sectional view of an insulator separating pluraltemperature control elements according to another embodiment;

FIG. 4A is a cross-sectional view of a substrate holder according toanother embodiment of the present invention;

FIG. 4B is a bottom view of a substrate holder according to anotherembodiment of the present invention;

FIG. 5A is a cross-sectional view of a substrate holder according toanother embodiment of the present invention;

FIG. 5B is a bottom view of a substrate holder according to anotherembodiment of the present invention;

FIG. 6A is a side view of a substrate holder according to anotherembodiment of the present invention;

FIG. 6B is a cross-sectional view of a substrate holder according toanother embodiment of the present invention; and

FIGS. 7A-7D illustrate various steps in a manufacturing method of thepresent invention; and

FIGS. 8A-8C illustrate top and cross-sectional views of anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals designateidentical or corresponding parts throughout the several views, FIGS. 2A,2B, 2C, and 2D illustrate a top view, a side view, a sidecross-sectional view, and a bottom view, respectively, of a substrateholder 40 for holding/supporting a substrate (e.g., a semiconductorwafer or a liquid crystal display panel) during processing in aprocessing environment. The substrate holder 40 includes a firsttemperature control element 41A and a second temperature control element41B.

The first and second temperature control elements 41A and 41B aresubstantially circular. For, example, each temperature control elementcan comprise a cooling channel for circulating a fluid at reducedtemperature, a heating channel for circulating a fluid at elevatedtemperature, a resistive heating element, an array of thermo-electriccoolers, etc. For clarity of presentation, the former temperaturecontrol elements (e.g., a cooling channel or heating channel) isexemplified in FIGS. 2C and 2D. Each temperature control element isrepresented by a temperature controlled cooling (or heating) channel(also referred to as a passageway) formed into the substrate holder 40.An insulator 43 is positioned between the first and second temperaturecontrol elements 41A and 41B. The insulator 43 is substantiallyconcentric with the first and second temperature control elements (tce)41A and 41B. Inlets 44 and outlets 45 (FIG. 2D) provide means forcirculating (counterclockwise for tce 41B and clockwise for tce 41A) thefluid (e.g. Flourinert, Galden, HT 135) through each temperature controlelement 41A, 41B, and in a quantity necessary to maintain the substrateholder 40 within a specified temperature range.

As shown in FIG. 2C, the temperature control elements 41A and 41B areformed substantially within the center of the substrate holder 40.Preferably, the temperature control elements 41A and 41B should beequidistant from the top of the substrate holder to the bottom of thesubstrate holder. For example, the substrate holder 40 has a depth fromthe top surface 42 a to the bottom surface 42 b of D₁. The depths fromthe top surface 42 a to the upper surface of the temperature controlelements 41A and 41B and from the bottom surface 42 b to the base of thecooling/heating elements 41A and 41B is D₂ and D₄, respectively. Thus,for example, the height of the temperature control elements 41A and 41Bis D₃ where D₃=D₁−D₂−D₄. However, as will be discussed later, the heightof the temperature control element can be variable. Alternately,fin-like projections 46 having a depth D₅ can extend towards the base ofthe temperature control elements 41A and 41B from the upper surface ofthe temperature control elements 41B and 41B. The fin-like projections46 provide additional wetted surface area through which heat may betransferred.

A thermal insulator 43 extends from nearly the top surface 42A to nearlythe bottom surface 42B. The insulator 43 has a substantially rectangularcross-section where the top end is parallel to the surface 42A and thebottom end is parallel to the surface 42B. The insulator 43 extends in acircle through the substrate holder 40 such that the temperature controlelements 41A and 41B are effectively thermally separated from oneanother. That said, although this invention contemplates that theinsulator 43 could extend all the way to the surfaces of the substrateholder 40, it is preferable that a thin layer of substrate holdermaterial remain at least above the insulator. This aids in thestructural integrity of the substrate holder 40.

An adhesive 47 can be used to bond the insulator 43 to the substrateholder 40; however, it is not necessary. The adhesive 47 should preventor substantially decrease leakage across the insulator 43 and maintain aseal for the life of the substrate holder 40. Preferably, the adhesive47 will also have heat transfer properties similar to the thermalinsulator 43. As such, the adhesive 47 can be made of some industrialgrade glue, a frit composed of fine alumina mixed with an adhesive, orwhere a quartz substrate holder is used, a frit composed of quartzpowder mixed with an appropriate base vehicle and thinner.

During higher temperature applications where radiative transport becomesmore significant, reflecting surfaces 48 may be applied to either sideof the insulator 43. The reflecting surfaces 48 further inhibit heattransfer from one side of the insulator 43 to the other side.

An alternate embodiment of the present invention is illustrated in FIG.3. According to this embodiment, an gaseous chamber 49 is shown servingas the insulator. The gaseous chamber 49 is preferably composed of asection of the substrate holder material extending from substantiallythe top surface 42A to substantially the bottom surface 42B. As above,the gaseous chamber 49 extends in a circle through the substrate holder40 such that the temperature control elements 41A and 41B areeffectively thermally separated from one another.

The space defined by the area inside the gaseous chamber 49 isconfigured to receive a gas at a predetermined pressure (e.g.,atmospheric pressure, vacuum pressure, or above-atmospheric pressure)and temperature. A piping system 50 couples the gaseous chamber 49 to agas supply with, for example, a pressure regulator and/or a pumpingsystem, other gaseous chambers, and possibly to the atmosphere. Thepiping system 50 may also connect the gaseous chamber 49 with a gassource extrinsic to the substrate holder so that a gas may be pumpedinto the air chamber 49.

The insertion of insulator 43 between temperature control elements 41Aand 41B can reduce the thermal transfer between the respective thermalzones by an amount in excess of 95%. The amount of heat transfer isrelated to the effective reduction in thermal conduction between the twoor more thermal zones by the insertion of insulator 43. This effectivereduction in the thermal conduction between the two thermal zones isprimarily attributed to the material properties of the insulator 43(e.g., thermal conductivity of insulator 43 relative to the thermalconductivity of the material comprising the substrate holder 40), thethickness of insulator 43, and the fraction of area separating the twothermal zones that is occupied by the insulator 43 (e.g., the insulator43 may not extend entirely to surfaces 42A and 42B in order to retainthe structural integrity of the substrate holder 40). For example, givenan insulator 43 of thickness equivalent to 2 mm and of height extendingto within 1 mm of the upper surface 42A and the lower surface 42B of a 5cm thick substrate holder 40, the percent reduction in heat transferbetween thermal zones is estimated in TABLE I for an insulator 43comprised of alumina, quartz, helium at standard temperature andpressure (STP), or helium at 1 mTorr. Additionally, as provided in TABLEI, the respective thermal conductivities used for approximating apercent reduction in heat transfer are presented.

TABLE I MATERIAL k (W/m-K) % REDUCTION Aluminum 237 NA Alumina 46 77.4Quartz 10.4 91.8 Helium (STP) 0.18 95.9 Helium (1 mTorr) 0.00018 96

Other arrangements of this embodiment include the use of a materialdifferent from the substrate holder material to support the gaseouschamber 49. Such material could include any material with heat transfercapabilities less than that of the substrate holder material. Forexample, the thermal insulating material employed in the firstembodiment, assuming that a seal for the gaseous chamber could bemaintained.

As in the first embodiment, reflecting surfaces 48 may be applied to thesides of the gaseous chamber 49 to further inhibit heat transfer on oneside of the gaseous chamber 49 on the other side.

The result of installing the insulators discussed above is asignificantly reduced degree of heat transfer through different zones ofthe substrate holder 40. To overcome shortcomings associated with asubstrate holder having a uniform temperature profile, the substrateholder in the present invention includes at least two thermal zonesacross the surface 42A which can correspond to the arrangement and shapeof the temperature control elements and the insulator(s) installed inthe substrate holder. Thus, the effects of temperature gradients can bemanipulated as necessary for a particular substrate process.

As shown in FIGS. 2A-D, and 3, the temperature control elements 41A and41B are concentric elements. These concentric elements can have aconstant cross-section along their length, or they can have anon-constant cross-section with length. Alternately, the temperaturecontrol elements can be radially extending elements as shown incross-sectional view in FIG. 4A and in bottom view in FIG. 4B. Forexample, the radially extending temperature control elements can befluid channels, each having an inlet 44 at a first radius and an outlet45 at a second radius.

With reference now to FIG. 4A, a cross section along the side of thetemperature control element is shown so as to illustrate a preferablearrangement of the temperature control element 41A and 41D (note, thedrawing is not to scale). The inlet 44 and outlet 45 are shown whereinthe cooling element depth at the inlet 44 is D₆ and the depth at theoutlet 45 is D₆′. Since the width of the radial spindle increases as onemoves radially outward, the depth is decreased from D₆ to D₆′ in orderto maintain the same cooling channel cross-sectional area. Due to massconservation, the constant area maintains a constant flow velocity. Ifthe depth is maintained constant, then the increase in area would resultin a decrease of the flow velocity hence leading to a decrease in theheat transfer coefficient. This is contrasted with what would be asignificant reduction in the heat flux associated with the reduction inthe flow velocity.

As an example, the coolant flow channels can be maintained throughoutwith an approximately constant cross-sectional area. This enables theconstant, nearly uniform flow throughout. A second order effect in thiscase is the slight reduction in hydraulic diameter with radius whichalso increases the heat transfer coefficient (only slightly) these twoeffects are necessary to aid in achieving a constant heat flux withradius (an increase in the heat transfer coefficient can balance theincrease in the cooling temperature). An alternate embodiment includes adecreasing cross-sectional area with an increasing radius. In this case,the insulator 43 can have a constant height D₁ along the length of theinsulator.

In accordance with this invention, the insulator 43 is shapedindependently of the shape of the cooling element. Thus, insulator 43will have a constant height nearly equal to the height of the substrateholder D, along the entire length of the insulator. Therefore, theinsulator maintains a nearly constant level of heat transfer reductionalong its entire length.

Alternately, as shown in FIGS. 5A and 5B, substrate holder 40 cancomprise a combination of azimuthally (or concentric) temperaturecontrol elements and radially extending temperature control elements.

An alternate arrangement of the present invention is shown in FIG. 6A.FIG. 6B is an exemplary quartz substrate holder as described in U.S.patent application Ser. No. 10/088,504 filed on Mar. 28, 2002, which isherein incorporated by reference. A set of substrate holder layersincluding an upper layer 100 and a lower layer 101 are shown. The upperlayer 100 can comprise a cylindrical plate (or cover plate). The lowerlayer 101 includes a plurality of cooling strips including inner coolingstrips 102 and outer cooling strips 103. Furthermore, the lower layer101 includes insulating strips including inner insulating strips 104,outer insulating strips 105, and concentric insulating strips 106, eachof which reside within receiving features formed within lower plate 101.The receiving features can be machined using techniques well known tothose skilled in the art of machining quartz.

Support structures 108 align each face with the other. When aligned, theinsulating strips 104, 105 fit within the inner cooling strips 102 andthe outer insulating strips 103. Therefore, the insulating strips 104,105 form thermal insulating zones within the cooling strips 102, 103.Once the cooling channels 102, 103, and the receiving features forinsulating strips 104, 105, 106 are machined, and the insulating stripsare inserted within the receiving features, the upper layer 100 can becoupled to the lower layer 101. For example, the coupling between upperlayer 100 and lower layer can be achieved using fusion bonding as isknown to skilled in the art of bonding quartz.

Still referring to FIG. 6B, the pattern of the cooling channel is shownwhereby particular sections of the substrate holder are cooled bylocalized cooling systems. Particularly inner cooling strip 102 issubstantially trapezoidal shaped. Thus it is narrow at the center of thesubstrate holder and becomes wider as the strip extends towards theouter sections of the substrate holder. Coolant for the cooling stripsenters the cooling strip of the inlets 109 and is pumped out by outlets110.

Alternately, where it is impractical to attempt to install thermal zonesinto a substrate holder, as in some of the arrangements of coolingstrips in U.S. patent application Ser. No. 10/088,504 filed on Mar. 28,2002, herein incorporated by reference, in which the cooling stripsconsist of a very narrow passage, the present invention can be modified.In this case the invention installed into the substrate holder wouldreplace substrate holder material between the stripes. This arrangementwould therefore be similar to the arrangement discussed above withreference to the aluminum substrate holders.

Because the material used in quartz substrate holders has a low thermalconductivity, it would be necessary for the insulator to have anextremely low thermal conductivity to be effective in preventing heattransfer. Certainly, the gaseous chamber or vacuum discussed above wouldqualify as potentially effective insulators.

Manufacture of a substrate holder according to one embodiment of thepresent invention involves generally 4 distinct steps (e.g., as shown inFIGS. 7A-7D). The substrate holder 40 is formed from an upper portion40A and a lower portion 40B. As illustrated in FIG. 7A, a section of theupper portion 40A of substrate holder 40 is removed to make room for thetemperature control elements 41A, 41B (and optionally forming fins 46).Thus, surface 42B must be penetrated such that the section of thesubstrate holder remaining has a depth, D₂ where the temperature controlelements 41A, 41B are envisioned. A section 61 of the substrate holder40 is removed to nearly surface 42 a where the insulator 43 is intendedto be installed.

Next, as shown in FIG. 7B, the insulator 43, including an (optional)adhesive 47 is inserted into the space created for it such that theadhesive 47 forms a good seal between the insulator 43 and the substrateholder 40.

Next, as shown in FIG. 7C, the upper and lower portions 40A and 40B,respectively, the substrate holder 40 are assembled so as to form floorsof the temperature control elements 41A, 41B. As shown in FIG. 7D, theseportions are then welded to form weld joint 203 on the substrate holder40 and creating the temperature control elements 41A, 41B.

As a result when assembled, the insulating strips divide the coolingstrips into thermal rows. Due to the high number of individual coolingstrips, spread across the surface of the substrate holder, the variousthermal zones provide an effective means for cooling specific areas ofthe substrate holder.

In an alternate embodiment, FIGS. 8A and 8B present a top view and sidecross-sectional view of a substrate holder 400. Substrate holder 400comprises a first array of temperature control elements 410A, 410B, and410C, and a second array of temperature control elements 420A, 420B, and420C. The first array of temperature control elements 410A-C can, forexample, comprise a fluid channel that permits the passage of a cooledor heated fluid for transferring heat from or to the substrate holder400, respectively. Additionally, the second array of temperature controlelements 420A-C can, for example, comprise an array of thermo-electricelements capable of heating or cooling a substrate depending upon thedirection of electrical current flow through the respective elements. Anexemplary thermo-electric element is one commercially available fromAdvanced Thermoelectric, Model ST-127-1.4-8.5M (a 40 mm by 40 mm by 3.4mm thermoelectric device capable of a maximum heat transfer power of 72W). The second array of temperature control elements 420A-C can beadapted for rapid control of substrate temperature, and, depending uponthe direction of heat flow, the first array of temperature controlelements 410A-C can be adapted to transfer heat to or remove heat fromthe backside of the second array of temperature control elements 420A-C.Furthermore, as illustrated in FIG. 8B, substrate holder 400 furthercomprises one or more thermal insulators 430A, 430B in order to providethermal insulation between respective temperature control zones. Eachthermal insulator 430A, 430B can comprise an annular space coupled to agas supply through one or more pressure control devices 450A, 450B.Additionally, each annular space can be coupled to at least one of achannel or array of gas distribution orifices 440A, 440B in order tocouple a gas supplied to the thermal insulator to the space residingbetween a back-side surface of the substrate and an upper surface of thesubstrate holder 400. The gas can, for example, comprise an inert gassuch as helium, argon, xenon, a process gas such as CF4, C4F8, C5F8,C4F6, etc., or any other gas such as hydrogen, oxygen, nitrogen, etc.Pressure control devices 450A, 450B can be utilized to control thepressure in the annular space of each thermal insulator 430A, 430B, andthe space residing between the back-side of the substrate and the uppersurface of the substrate holder 400.

Alternately, as illustrated in FIG. 8C, an additional thermal insulator430C can be utilized to distribute a gas to the center region of thesubstrate through an additional pressure control device 450C.

Alternately, each thermal insulator 430A, 430B, and 430C is coupled to asingle gas supply device with a single pressure control device.

As would be understood by one of ordinary skill in the art, theapplication of gas to the backside of a wafer via thermal insulators isnot limited to the embodiment of FIGS. 8A-8C. Any of FIGS. 1-7 can bemodified to include at least one thermal insulator 430 in addition to orin place of their corresponding illustrated insulators.

Although only certain exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention.

1. A thermally zoned substrate holder, comprising: a base upper portionhaving top and bottom surfaces, the top surface configured to support asubstrate and the bottom surface having a recess formed therein; aplurality of temperature control elements inside the recess, eachelement having a top surface seated in the recess and a bottom surfaceforming a floor of said recess; at least one thermal insulator having alower coefficient of thermal conductivity than a material of the base,the at least one insulator being positioned within said recess anddisposed between the plurality of temperature control elements andsubstantially thermally separating the plurality of temperature controlelements; and a base lower portion positioned within said recess andseated to said floor of said recess to substantially fill said recess,wherein the at least one insulator comprises a gas chamber configured toreceive a gas at a predetermined pressure via a piping system disposedin the base upper portion which couples the gas chamber to an externalgas supply.
 2. The apparatus of claim 1, wherein said chamber has across-sectional width of approximately 2 mm.
 3. The apparatus of claim1, wherein said chamber comprises support material different from saidbase.
 4. A thermally zoned substrate holder, comprising: a base upperportion having top and bottom surfaces, the top surface configured tosupport a substrate and the bottom surface having a recess and a pipingsystem formed therein; a plurality of temperature control elementsinside the recess, each element having a top surface seated in therecess and a bottom surface forming a floor of said recess; at least onethermal insulator having a lower coefficient of thermal conductivitythan a material of the base, the at least one insulator being positionedwithin said recess and disposed between the plurality of temperaturecontrol elements and substantially thermally separating the plurality oftemperature control elements; and a base lower portion positioned withinsaid recess and seated to said floor of said recess to substantiallyfill said recess, wherein said at least one insulator extends withinapproximately 1 mm of said top and bottom surface and said at least oneinsulator comprises a reflective surface.